Hi Guys,
I'm looking at the Sigma 18-50mm F2.8 Macro EX DC HSM zoom lens for a project.
I know that the lens is an internal focusing unit, but I am trying to find out if it is also an "Internal Zooming" unit ?
On the Sigma web-site page it says that the front lens doesn't rotate during focusing, and this usually means that it is an internally zooming lens,
but the stats don't say that it is internal zoom and they usually report this.

Does anyone have one of these 18-50mm macro HSM lenses that they can reliably report whether it is/isn't an internal zoomer?
If it is NOT an internal zoomer, could you please let me know how far the lens extends when fully zoomed out?

Thanks for taking the time folks, your help is gratefully received,
Bruce...

According to the lens chart on the Sigma web site the length varies from 85.8mm to 101.5mm over the zoom range for the non-HSM version. They don't quote a fully extended length for the HSM version but I believe it would be similar:

http://www.sigma-photo.com/lenses/lenses_chart.asp

Gudge,
Thanks for the chart; it's exactly what I have been looking for.



Bruce,

I am glad to see you are interested in the 18-50 as I am. Please note that there might be an error on this chart. The 18-50 f/2.8 HSM Macro min. focus is 28 cm, but in the lens specs it is 20 cm just like the non HSM version. Also the AoV is wrong on the chart. Without the lenses in hand, I can not see how many people can not fit the 17-70 HSM versions in their housings, the non HSM will work. ???



Please keep us posted.



Regards,

Bob

Hi Guys,
Thanks for the replies, and that chart you gave us Gudge is one of the 'gems' that is usually hidden from view in cyberspace.
Here is the reply that I got from Sigma in the USA, and I would like to publicly thank Desiree Gaige for her response to my questions.
And once again I would like to publicly speak out about the bloody apathy of Oz dealer networks. In this case C.R.Kennedy, who are the Oz
distributors of Sigma, are bloody pathetic.
Anyway, back to team America and Desiree:

Thank you for your interest in Sigma products.

The lens is not internal zoom type.

Here are measurements.

For Canon

18mm position ... 85mm

50mm position ... 111mm

For Nikon

18mm position ... 82.5mm

50mm position ... 107.5mm

Does not include bayonet

I have been looking at the 18-50 F2.8 HSM as a mid range zoom/macro lens. On my D70S it looks like it will work at around the 30-75mm range that will focus down onto the front port (nearly) and before I forget, this lens is to be used for macro and NOT wide-angle and will therefore be behind a flat port which will also give me a 'tad' more magnification. I'm not familiar with the mathematics of the extra magnification from the flat port verses the dome port, but if some-one would like to chime in, I'd be very happy for my own information.
My next step will be to add a Kenko 1.4 T/C to the set-up and give the 18-50 a bit more grunt and into the 45-112 zoom range and again with a 'tad' more from the flat port.
This will take the fixed F2.8 to a fixed F4 and this will result in a lens that is still 'faster' than the 17-70mm Sigma.
My only problem now will be to find a zoom gear that will fit the 18-50 and be long enough to take in the 1.4 T/C as well? Anyone got any ideas on that front for me?

Bruce...

I've been using the Sigma 18-50 f2.8 for the last two years. I've not had the HSM version but I gather optically they are identicle.

I've been a big fan of this lens and have got some great results from it behind both a dome port and flat port. Even though I've just sold it I reckon it has been superb. I never went for the 17-70 Sigma as it was too long to house as effectively. I really can't see a better mid range zoom out there at the moment for an APS sensor.

Behind a dome port and a 40mm extension ring and the whole of the zoom range was useable - corner sharpness seemed OK at the wide end although there might have been quite a curved depth of field.

The more I used it, the more I prefered using it behind a flat port. The only dissapointment was that I could only use a restricted zoom range of between 24 to 38 mm. Wider than 24mm and it would vingnette and longer than 38 and it would be against the glass port.

The min focus of 20 cm is superb and I'm amazed why people bother to house lenses like the expensive Nikkor 17-55 and 17-35 with their poor close focus ability.

For a zoom gear I used one that fitted my Tokina 10-17 zoom together with a couple of elastic bands for padding out the gap. The AF/MF switch is a bit of a pain as it gets in the way, but not too bad.

I only sold it as I am planning to give the newish Tokina 35mm macro a go as an alternative.

Hope that helps, Trev

Bruce,

I am glad to see that you are doing your homework. I'll "chime in" on the air/saltwater interface magnification with a flat port knowing full well that the slightest error will be corrected by someone on this form. Mas o menos - multiply by 1 -1/3; e.g. 18 becomes 24 mm and 50 becomes 65 mm.

Once you select the version of the lens you want (HSM or non HSM), measure the zoom ring diameter and there will likely be a Nexus gear that will work; likewise with the T/C. If you can't get the help you need in Oz, I'll contact my Nexus supplier. I will need the same info (may be not for the T/C). If that fails, I have fabricated zoom gears from the ikelite plastic zoom/focus kit.

Regards,

Bob

Trevor,

Thanks loads for the information. Please allow me to trouble you for a bit more? What are the diameters of the flat and dome ports?

TIA

Regards,

Bob

Hey guys,
I also use this lens (the HSM version) on my D200 and there is one extra thing you probably should be aware of. I destroyed several gear wheels inside my housing with this lens. It might be a specific Hugyfot problem but the zooming of this lens is less smooth then with all my other zoomlenses. The problem is that you'll have to use more force then with most other zoomlenses because its relatively heavy (and fat BTW). Fortunately, Hugyfot provided me some spare gearwheels so i can replace it when it's finished. If your housing is equiped with all metal gears i think you won't experience any problems, but my Hugy has both metal and plastic gear wheels and the metal gear 'eats' the plastic gear. FYI, i use the 18-50 mm behind a domeport and i can use the full zoom range with corner to corner sharpness with the diaphragm closed 1 or 2 stops (btw this is also true when used topside).
But there's one other question i have about this lens: if i use the 18-50 mm at 50 mm it still has a wider angle then my prime 50 mm macro lens, is there something that i don't understand, or is Sigma just allowing their lenses to have a large deviation.

cheers, Udo

Bob,

Not sure how this helps you but my Sea & Sea ports measure 97mm in diameter at the housing end.

Unlike Udo I had no problem with the zooming other than getting a zoom gear not to foul the small switch on the lens.

I should add that I was actually very happy with performance behind the dome port but that I just prefered using it behind a flat port even with a restricted zoom range.

One other thing - The front of the Sigma lens has quite a wide front - intially it was fouling against a curious plastic part inside the front of my flat port (Sea & Sea NX flat port). I fixed this by grinding it down. This probably only makes sense to Sea & Sea users who have this particular port. I read a while back that others have done the same thing to get other fat lenses to fit.

Hi Trevor,



My mistake for not being precise. I am referring to the port front diameter, e.g. my flat port diameter is 110 mm and the dome port diameter is 170 mm or whatever. My concern is image vignetting in the flat port. I use an old Sigma 28-80 "macro" lens in the 110 mm flat port w/o vignetting the image. Of course 18 mm is much wider than 28 mm and my dinky lens is much smaller than the 18-50. I'll try to do some measurements on my lens this evening.

"I fixed this by grinding it down" – ouch, my 110 mm port does not have this, but is worth considering a larger port configuration (M5, M6).

Regards,
Bob

Curious, what did you use to grind that node down, dremel type tool? Think it is going to be in the way when I mount a 105mm VR.

Response from Sigma Photo (USA): "
The posted dimensions include maximum diameter, which in this case would be
front barrel diameter. The HSM and non-HSM versions do differ in their
diameters , in the mid-barrel area (because of the space required for the
HSM), but in each case the diameters are smaller than the front barrel, so
the published specs are the same. "

Yes, the front of the lens is the largest. That is apparent from the pictures on the Sigma site. I'll try to find out the mid-barrel dimensions.

Regards,

Bob

[quote name='Eyematey' date='Oct 29 2008, 02:43 PM' post='189502']
Curious, what did you use to grind that node down, dremel type tool? Think it is going to be in the way when I mount a 105mm VR.

I used a sharp chisel. It's a bit like slicing cheese. Suggest you lay something thin and flat against the glass for protection in case you slip with the chisel. A dremel sounds a bit messy to me. It really is very easy to make a very neat job. Now there is room for those fat lenses like the Sigma 18-50 inside my Sea& Sea NX flat port.

*gone hunting for a chisel*.....since I have the 18-50 HSM and a 105VR......

I used a dremel, covered glass with paper towel. Node gone 105vr fits fine. May use a chisel to make it look more uniform, good idea. Also made a focus gear for the 105vr, tight fit.

Eyematey,

There is another thread running elsewhere at the moment about 'custom/DIY' focus gears.
I will be making my own zoom gear for this lens. Would you care to show/tell us how you
made up your gear for the 105mm VR?
It would be great if you could include some pics...

Bruce...

Yo Bruce,

Did you get the Sigma 18-50 lens? If so, which version HSM or non HSM? Please measure the diameter of the zoom ring and post. TIA.
Regards,
Bob